1. Field of the Invention
The present invention relates to a color registration adjusting method in an image forming apparatus, and more particularly, to a color registration adjusting method in an image forming apparatus for electronically adjusting color registration of a main scanning direction using an edge forming algorithm of a photoreceptor belt.
The present application is based upon Korean Application No. 97-36871, which is incorporated herein by reference.
2. Description of the Related Art
An image forming apparatus reproduces characters or images onto a recording medium according to transferred characters or image data signals, and generally includes a photoreceptor member (e.g., a photoreceptor drum or a photoreceptor belt) for forming a latent electrostatic image, a charging unit for charging the photoreceptor member, an exposing unit for forming a latent electrostatic image having a predetermined pattern by scanning light on the charged photoreceptor member, a developing unit for developing the latent electrostatic image by supplying a developing medium, e.g., a toner or a developer liquid, on the exposed latent electrostatic image, and a transfer member for transferring the developed image to the recording medium by applying pressure or heat.
FIG. 1 is a schematic diagram of a general image forming apparatus.
Referring to FIG. 1, the general image forming apparatus includes a photoreceptor belt 104 installed to be capable of circulating around first, second and third belt rollers 101, 102 and 103, a discharger 105 for removing charges remaining on the photoreceptor belt 104, a charger 106 for newly generating charges on the photoreceptor belt 104, exposure units 107, 108, 109 and 110 each having a laser scanning unit (not shown) which scans a laser beam across the photoreceptor belt 104 to selectively discharge the image forming portion of the photoreceptor belt 104 to be formed into an image shaped pattern, development units 111, 112, 113 and 114 for developing the latent electrostatic image formed on the photoreceptor belt 104 using a developer liquid, a drying unit 115 for drying the developer liquid supplied to the latent image, and a transfer unit 116 for transferring a developed image formed on the photoreceptor belt 104 to a recording medium 117 such as a recording sheet or a film.
Here, the development unit 111 includes a development roller 111a for coating the developer liquid on the photoreceptor belt 104, a developer liquid supplier 111b for supplying the developer liquid to the development roller 111a, a cleaning roller 111c for eliminating the developer liquid embedded on the rear surface of the development roller 111a, first and second squeegee rollers 111d and 111e for eliminating the developer liquid remaining on the photoreceptor belt 104, first and second blades 111f and 111g for eliminating the developing embedded on the first and second squeegee rollers 111d and 111e, and a developer liquid recovery reservoir 111h for recovering the developer liquid removed by the cleaning roller 111c and the blades 111f and 111g. The drying unit 115 includes a heating roller 115h for drying the developer liquid embedded on the photoreceptor belt 104. The transfer unit 116 includes a transfer roller 116t closely pressing against and rotating relative to the first belt roller 101 with the photoreceptor belt 104 interposed therebetween for receiving the image on the photoreceptor belt 104, and a fixing roller 116p closely pressing against and rotating relative to the transfer roller 116t, for fixing the image transferred to the transfer roller 116t onto the recording sheet 117.
In the image forming apparatus having the aforementioned configuration, error factors related to laser beam scanning will be described.
First, the state of the respective edge detectors for colors Y (yellow), M (magenta), C(cyan) and K (black), provided in the photoreceptor belt 104, will be described. As shown in FIG. 2, based on a Y-belt edge detector 201, the respective M-, C- and K-belt edge detectors 202, 203 and 204 are not aligned along a straight line. Thus, an error is generated by the scanning of the laser beam. In this case, if the resolution of the main scanning direction, i.e., perpendicular to the traveling direction of the photoreceptor belt, is 600 dpi, the precision in the installation (arrangement) of the belt edge detectors must be at least within 1/600 inch. If the amount of mis-registration of color is intended to be within 1/5 of a pixel, the precision in the arrangement of the Y-, M-, C- and K-belt edge detectors along a line must be within 1/(5.times.600) inch. However, it is almost impossible to adjust the detectors mechanically with such precision. Thus, the detectors must be adjusted electronically.
Next, as shown in FIG. 3, the respective scanners 301, 302, 303 and 304 for colors Y, M, C and K are not aligned along a straight line, which causes an error in scanning a laser beam. This is also very difficult to correct mechanically.
Another error factor in the laser beam scanning is belt weaving. Even when the photoreceptor belt 104 is steered while being driven, variance is generated in the main scanning direction, which causes an error in scanning a laser beam.
Finally, a defect of the photoreceptor belt 104 itself may be involved in the error related to the laser beam scanning. In other words, if the edges of the photoreceptor belt 104 are not straight, an error is generated in scanning the laser beam across the photoreceptor belt.
The above-described error factors cannot be corrected mechanically, and must be corrected electronically, instead.